The invention relates generally to the field of data processing. More specifically, the invention relates to a method for detecting the format of video data and processing the video data based on the detected format.
Various formats exist for television data. Much of the National Television System Committee (NTSC) formatted content broadcast on terrestrial or cable television is entirely or partially shot on film (movies, sitcoms, music videos, commercials, etc.) and then later converted to NTSC video format by 3:2 pulldown. 3:2 pulldown is the process by which 24 frames/sec film content is converted into 59.94 fields/sec video. As used herein, “3:2 content,” “3:2 pulldown clips,” “3:2 sequences,” and “telecine sequences” indicate video data that was generated from film using the 3:2 pulldown process. “Standard video” will be used to indicate video data that did not originate from film.
When converting from film to video using the 3:2 pulldown process, two film frames, 102 and 104, generate five interlaced video fields, 106, 108, 110, 112 and 114, as depicted in FIG. 1. In addition, the film speed is slowed down by 0.1% to 23.976 (24/1.001) in order to account for the fact that NTSC video runs at 29.97 frames/sec. The process of converting from 3:2 content back to film is called inverse 3:2 pulldown (also known as inverse telecine).
The two primary applications of inverse 3:2 pulldown are display and compression. In terms of display, inverse 3:2 pulldown facilitates the optimal display of film content on a progressive monitor (such as a large-screen rear-projection system, a liquid crystal display, or a flat panel plasma display) because it allows each film frame to be displayed in its original progressive form for a uniform and consistent duration of 1/24th of a second. In terms of compression, inverse 3:2 pulldown results in better compression efficiency and reduced computational complexity in a video encoder because it allows telecine content to be encoded at 24 frames/sec format rather than at 59.94 fields/sec.
Known methods can detect 3:2 content and extract the original film frames where the repeated field pattern is uninterrupted and distinct. However, there are several factors that produce unreliable results in known systems and methods for detecting 3:2 content or other video formats.
For example, known techniques do not reliably distinguish between repeated fields and non-repeated fields when the motion of objects is very small (providing little field-to-field positional difference) and/or the video noise is high. Moreover, it is not uncommon that Digital Video Disks (DVD's) and other video sources contain both standard video and 3:2 content In such cases, it is difficult for known algorithms to detect the location of standard video/3:2 content transitions and respond accordingly. In addition, with known techniques, standard video that is inverted can result in highly objectionable artifacts resulting from weaving two fields from different time instants. Moreover, the phase of the 3:2 pulldown pattern may change when two different 3:2 pulldown clips are spliced together, e.g., at a scene transition. Ambiguous situations arise, for example, when one 3:2 pulldown clip is transitioned to another 3:2 pulldown clip via a fade. This editing can result in the superposition of two 3:2 patterns with different phases, which cannot be unambiguously inverted using known methods. Furthermore, some content providers broadcast 60 fields/sec video that has been generated using a non-standard 3:2 pulldown approach. One example of such a process is varispeed, which alters the run time of a program. Simply repeating film frames would cause stutter, so, instead, the 3:2 pattern is modified to ensure a smooth temporal rate. Known detection methods are ill-suited to detect such non-standard video formats.
Therefore, a need exists for a system and method that can produce more reliable detection of video format where, for example, the source video is noisy, or where the video data pattern is interrupted by the use of splices or transitions, or where the video is otherwise altered by a content provider.